1. Field of the Invention
The invention relates to expansion control struts and piston ring groove protectors as employed in internal combustion engines.
2. Background of the Invention
Internal combustion engine pistons are made from aluminum alloys having relatively low expansion and sufficient hardness for good machinability. Such pistons include a head portion having piston ring grooves and a skirt portion extending therefrom.
Ring groove protectors are often provided to protect the pistons, particularly in engines which are subject to long periods of use at full loads. Truck engines, tractor engines, and industrial engines are commonly so equipped. In the absence of such protection, the ring grooves could enlarge vertically and thereby damage the piston rings. An armored groove does not tend to enlarge. Ferrous ring groove protectors are well known for this purpose.
Expansion control steel struts are employed in conjunction with aluminum pistons for controlling the thermal expansion thereof. They are cast in the piston to control the radial expansion of the piston skirt during temperature changes. When the molten aluminum solidifies about the struts, a bimetallic action is created which causes the aluminum thrust faces to expand at a slower rate than the cast iron bore within which the piston is located. As the engine cools, these thrust faces contract at a slower rate than the bore. This decreases skirt to bore clearance and minimizes "cold slap."
Ring groove protectors and expansion control struts have generally been constructed as separate articles. The struts are cast in the piston and the groove protectors are assembled by hand. Alternatively, the groove protectors may be cast in the piston head as discussed in U.S. Pat. No. 3,512,791.
A groove protector and strut assembly may also be provided as an integral unit as disclosed in U.S. Pat. No. 3,535,986. Such an arrangement facilitates the manufacturing process as the entire unit is placed in a mold prior to casting.